Thank you for getting back to us with more precisions of what you have tried to fix the issue. In addition I've found more information that could help you bypass this error.
First of all, could you try editing this skin, exporting it with a new name, then uploading this new exported skin. It should allow you to open it properly without the error.
Also, to investigate this further and as I saw you already mentioned receiving this error when the file was too big, which can indeed happen, can you tell us what is the size of the skin you're trying to access?
Do not hesitate to come back to us with the result of this step and more information if the issue persists!